a) Field of the Invention
The present invention relates to a position measuring device of an electromagnetic actuator for an electromagnetically operated engine valve drive system and a method for attaching the same.
b) Description of the Related Art
A cam shaft drive system has still been dominated in an open-and-closure drive of intake and exhaust valves of an electronically controlled internal combustion engine although the electronically controlled engine has been adopted in automotive vehicles.
As the electronically controlled engine has become generalized, an application of an electronic control system to the open-and-closure drive system for the intake and exhaust valves has strongly been demanded from standpoints of a further improvement in a fuel consumption and an exhaust gas purification.
To meet this demand, a U.S. Pat. No. 5,769,043 issued on Jun. 23, 1998 to James A. Nitkiewicz has proposed an apparatus for electromagnetically driving the intake and exhaust valves to open and close intake and exhaust ports of the engine using an electromagnet actuator, viz., an electromagnetically operated engine valve drive system.
In the above-described electromagnetically operated engine valve drive system, independent controls of both of a valve open timing and a valve closure timing and, furthermore, a valve displacement control are made possible.
These valve open-and-closure timing and valve displacement controls can optimally be made under various engine driving situations. To achieve this, it is necessary to detect accurately a position of a movable section of the electromagnetic actuator which reciprocates at a high velocity so that the valve displacement of the intake or exhaust valve can be recognized.
In this case, it is generally necessary to measure an instantaneous position of the movable section of the actuator with an extremely high accuracy and with no contact over a considerably long stroke. To meet this necessity, a position measuring device utilizing a Hall effect has been used in the above-described electromagnetically operated engine valve drive system. A kind of the position measuring device includes a magnetic field generating and detecting device (coupler) of a permanent magnet and a Hall effect device.
A Japanese Patent Application First Publication No. Heisei 6-180242 published on Jun. 28, 1994 exemplifies an area airflow meter to which the above-described position detecting device of the permanent magnet and Hall effect devices (or magnetic resistance elements) is applied.
In the above-identified Japanese Patent Application First Publication, one of the permanent magnet and the magnetic field detecting device, for example, the permanent magnet is attached onto its movable section, a strength of the magnetic field that the permanent magnet creates is measured by the attached magnetic field detecting device so that the position of the movable section can be measured.
In the above-described previously proposed electromagnetically operated engine valve drive system, no consideration is given to an attaching of the permanent magnet onto the movable section of the valve actuator so that a reduction in a reliability cannot be avoided and a maintenance of a measuring accuracy becomes difficult.
Since, in the previously proposed electromagnetically operated engine valve drive system, the movable section of the actuator has a considerably high velocity in the vicinities of start and end points of the stroke by which the movable section can be moved. Hence, if the movable section collide with a stationary section of the actuator at a high velocity region at proximities to the start and end points of the stroke, a large impulsive (collision) force due to an acceleration reaching up to several thousand""s G (gravity) would be received.
Therefore, in order to avoid an occurrence of the collision, to suppress the collision velocity to be low even when such a collision as described above has occurred, to reduce a noise or shock, or to achieve a long extension of life, a velocity variation control during the stroke has been applied such that the position of the movable section is measured and the velocity of the movable section is slowed down at proximities of start and end points of the stroke.
However, even if the velocity variation control has been applied, the occurrence in the collision of the movable section with the stationary section cannot be avoided when an initial adjustment of the device is carried out or when an abnormality in a controller for controlling the electromagnetically operated engine valve drive system occurs although no collision may occur in a steady state.
Since no consideration for the attaching of the position detecting permanent magnet with respect to the movable section of the valve actuator is given, so that a reliability of the permanent magnet would be reduced.
At this time, it is a general practice that the movable section of the actuator is made of a ferromagnetic material such as a steel integrated with a movable element such as an armature for electromagnets.
In the above-described previously proposed position detecting devices, no consideration for the attaching of position detecting permanent magnet onto the movable section of the actuator is given so that a disturbance of the magnetic field due to the permanent magnet occurs and the measurement accuracy can be reduced.
It is, hence, an object of the present invention to provide improved position measuring device for the electromagnetically operated engine valve drive system and method for attaching the same which can sufficiently suppress a reduction of a reliability in the attaching of the position detecting device onto the movable section of the electromagnetically operated engine valve drive system and can sufficiently suppress a reduction of a position measuring accuracy due to the attaching of the permanent magnet onto the movable section of the actuator with a simple structure.
According to one aspect of the present invention, there is provided a method for attaching a position measuring device of an electromagnetic actuator for an electromagnetically operated engine valve drive system, the electromagnetic actuator comprising: a movable section associated with an engine valve; and a permanent magnet used to detect a displacement position of the movable section, the method comprising attaching the permanent magnet onto the movable section via such a predetermined material as to have a lower hardness than that of the movable section.
According to another aspect of the present invention, there is provided a position measuring device of an electromagnetic actuator for an electromagnetically operated engine valve drive system, the position measuring device comprising: a movable section associated with an engine valve; and a permanent magnet attached onto the movable section via such a predetermined material as to have a lower hardness than that of the movable section to detect a displacement position of the movable section.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.